Merge 49883997d8 into 645a76e5b0

* Drop support for Go versions older than 1.10
* Remove 1.18 from test suite

.github/workflows/ci.yml

@@ -1,11 +1,15 @@
 name: ci
-on: [push]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
 jobs:
   ci-job:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go: [ '1.7.x', '1.18', '1.19', '1.20', '1.21', '1.x' ]
+        go: [ '1.10.x', '1.19', '1.20', '1.21', '1.22', '1.x' ]
     name: Go ${{ matrix.go }}
     steps:
       - uses: actions/checkout@v4

README.md

@@ -8,6 +8,8 @@ Arbitrary-precision fixed-point decimal numbers in go.
 
 _Note:_ Decimal library can "only" represent numbers with a maximum of 2^31 digits after the decimal point.
 
+_Note:_ The library does not remove trailing zeros when parsing decimals from strings, e.g., `1.18` does not internally equal `1.1800` when parsing with this library, see example in usage
+
 ## Features
 
  * The zero-value is 0, and is safe to use without initialization
@@ -22,7 +24,7 @@ Run `go get github.com/shopspring/decimal`
 
 ## Requirements 
 
-Decimal library requires Go version `>=1.7`
+Decimal library requires Go version `>=1.10`
 
 ## Usage
 
@@ -59,6 +61,32 @@ func main() {
 }
 ```
 
+Conservation of precision with trailing zeros. This conservation is, however,
+not translated backwards when printing the decimal as string.
+
+This is important to know.
+
+```go
+package main
+
+import (
+	"fmt"
+	"github.com/shopspring/decimal"
+)
+
+func main() {
+	noZeros := "1.18"
+	trailingZeros := "1.1800"
+
+	d1 := decimal.RequireFromString(noZeros)
+	d2 := decimal.RequireFromString(trailingZeros)
+
+	fmt.Println(d1.Coefficient(), d1.Exponent()) 	// 118 -2
+	fmt.Println(d2.Coefficient(), d2.Exponent()) 	// 118 -4
+	fmt.Println(d1)					// 1.18
+	fmt.Println(d2)					// 1.18
+```
+
 ## Documentation
 
 http://godoc.org/github.com/shopspring/decimal

decimal.go

@@ -1224,14 +1224,33 @@ func (d Decimal) Ln(precision int32) (Decimal, error) {
 }
 
 // NumDigits returns the number of digits of the decimal coefficient (d.Value)
-// Note: Current implementation is extremely slow for large decimals and/or decimals with large fractional part
 func (d Decimal) NumDigits() int {
-	d.ensureInitialized()
-	// Note(mwoss): It can be optimized, unnecessary cast of big.Int to string
-	if d.IsNegative() {
-		return len(d.value.String()) - 1
+	if d.value == nil {
+		return 1
 	}
-	return len(d.value.String())
+
+	if d.value.IsInt64() {
+		i64 := d.value.Int64()
+		// restrict fast path to integers with exact conversion to float64
+		if i64 <= (1<<53) && i64 >= -(1<<53) {
+			if i64 == 0 {
+				return 1
+			}
+			return int(math.Log10(math.Abs(float64(i64)))) + 1
+		}
+	}
+
+	estimatedNumDigits := int(float64(d.value.BitLen()) / math.Log2(10))
+
+	// estimatedNumDigits (lg10) may be off by 1, need to verify
+	digitsBigInt := big.NewInt(int64(estimatedNumDigits))
+	errorCorrectionUnit := digitsBigInt.Exp(tenInt, digitsBigInt, nil)
+
+	if d.value.CmpAbs(errorCorrectionUnit) >= 0 {
+		return estimatedNumDigits + 1
+	}
+
+	return estimatedNumDigits
 }
 
 // IsInteger returns true when decimal can be represented as an integer value, otherwise, it returns false.
@@ -1387,9 +1406,7 @@ func (d Decimal) IntPart() int64 {
 // BigInt returns integer component of the decimal as a BigInt.
 func (d Decimal) BigInt() *big.Int {
 	scaledD := d.rescale(0)
-	i := &big.Int{}
-	i.SetString(scaledD.String(), 10)
-	return i
+	return scaledD.value
 }
 
 // BigFloat returns decimal as BigFloat.

decimal_bench_test.go

@@ -121,6 +121,34 @@ func BenchmarkDecimal_RoundCash_Five(b *testing.B) {
 	}
 }
 
+func numDigits(b *testing.B, want int, val Decimal) {
+	b.Helper()
+	for i := 0; i < b.N; i++ {
+		if have := val.NumDigits(); have != want {
+			b.Fatalf("\nHave: %d\nWant: %d", have, want)
+		}
+	}
+}
+
+func BenchmarkDecimal_NumDigits10(b *testing.B) {
+	numDigits(b, 10, New(3478512345, -3))
+}
+
+func BenchmarkDecimal_NumDigits100(b *testing.B) {
+	s := make([]byte, 102)
+	for i := range s {
+		s[i] = byte('0' + i%10)
+	}
+	s[0] = '-'
+	s[100] = '.'
+	d, err := NewFromString(string(s))
+	if err != nil {
+		b.Log(d)
+		b.Error(err)
+	}
+	numDigits(b, 100, d)
+}
+
 func Benchmark_Cmp(b *testing.B) {
 	decimals := DecimalSlice([]Decimal{})
 	for i := 0; i < 1000000; i++ {
@@ -132,7 +160,7 @@ func Benchmark_Cmp(b *testing.B) {
 	}
 }
 
-func Benchmark_decimal_Decimal_Add_different_precision(b *testing.B) {
+func BenchmarkDecimal_Add_different_precision(b *testing.B) {
 	d1 := NewFromFloat(1000.123)
 	d2 := NewFromFloat(500).Mul(NewFromFloat(0.12))
 
@@ -143,7 +171,7 @@ func Benchmark_decimal_Decimal_Add_different_precision(b *testing.B) {
 	}
 }
 
-func Benchmark_decimal_Decimal_Sub_different_precision(b *testing.B) {
+func BenchmarkDecimal_Sub_different_precision(b *testing.B) {
 	d1 := NewFromFloat(1000.123)
 	d2 := NewFromFloat(500).Mul(NewFromFloat(0.12))
 
@@ -154,7 +182,7 @@ func Benchmark_decimal_Decimal_Sub_different_precision(b *testing.B) {
 	}
 }
 
-func Benchmark_decimal_Decimal_Add_same_precision(b *testing.B) {
+func BenchmarkDecimal_Add_same_precision(b *testing.B) {
 	d1 := NewFromFloat(1000.123)
 	d2 := NewFromFloat(500.123)
 
@@ -165,7 +193,7 @@ func Benchmark_decimal_Decimal_Add_same_precision(b *testing.B) {
 	}
 }
 
-func Benchmark_decimal_Decimal_Sub_same_precision(b *testing.B) {
+func BenchmarkDecimal_Sub_same_precision(b *testing.B) {
 	d1 := NewFromFloat(1000.123)
 	d2 := NewFromFloat(500.123)
 

go.mod

@@ -1,3 +1,3 @@
 module github.com/shopspring/decimal
 
-go 1.7
+go 1.10